Semiconductive magnetoresistance (MR) element has the characteristics of high compactness, non-contact, high sensitivity, long useful life and having only two leads on the ends. Such characteristics render semiconductive magnetoresistance element highly desirable for applications in, for example, speed sensor, potential sensor, position sensor and graph identification sensor. Indium antimonide compound, having the highest electron mobility, is the most commonly used material for producing semiconductive magnetoresistance element.
Presently, commercialized magnetoresistance products are most commonly produced employing the technique developed by Weiss et al in which an indium antimonide/nickel antimonide two phase single crystal is used as the magnetoresistance material. However, the intolerable high costs of the growth of indium antimonide single crystal and the accompanied grinding and polishing processes render its industrial applications impractical. Facing the deficiency, extensive research has been devoted to the development of indium antimonide film as a substitute for conventional indium antimonide single crystal. However, in the production of indium antimonide film, antimony tends to diffuse and evaporate from indium antimonide film and thus deteriorate the quality of the thus produced indium antimonide film. It is therefore still an issue to produce indium antimonide film having properties and sensitivity competitive with those of indium antimonide single crystal.
Excellent magnetoresistance elements are characterized by high electron mobility and well designed short circuit electrodes which are essential for obtaining high resistance variation due to the presence of magnetic field. To obtain a magnetoresistance element of high sensitivity, it is necessary to add external Hall voltage short circuit electrodes or, as a substitute for the external Hall voltage short circuit electrodes, introducing a second phase of needle-like precipitates having metallic conductivity. This adds further complexity to the production of magnetoresistance elements. A satisfactory process for producing high sensitivity magnetoresistance element has always been lacking.
The basics and drawbacks of the common processes for producing magnetoresistance element from indium antimonide single crystal and from indium antimonide film are described below.
With respect to the production of magnetoresistance element from indium antimonide single crystal, an indium antimonide single crystal wafer is grounded until a thickness below 50 .mu.m is obtained and then etched to impart the desired pattern. To obtain a high sensitivity indium antimonide single crystal with high R.sub.B /R.sub.o (the ratio of resistance value in the field to that in zero field) value, Hall voltage short circuit electrodes are often externally electroplated or evaporated to the pattern. In other cases the co-precipitation properties of indium antimonide and nickel antimonide are utilized that needle-like nickel antimonide is precipitated from the indium antimonide base in the production of indium antimonide single crystal as a substitute for the external Hall voltage short circuit electrodes. The techniques suffer primarily from the high costs of indium antimonide single crystal and the accompanied grinding and polishing of the crystal. Besides, large amount of materials is wasted during the grounding operation. On the other hand, it is very difficult to control the spatial uniformity of the needle-like precipitation of nickel antimonide in the Czchralski growth for the production of indium antimonide/nickel antimonide single crystal. As a result, the nickel antimonide precipitates will not disperse evenly or even emerge as aggregates, rendering the properties of the thus produced magnetoresistance element highly unidentical.
With respect to the production of magnetoresistance elements from indium antimonide film, different deposition ratios for indium, antimony or indium antimonide are controlled during the deposition process. A stepwise vapor deposition and an additional step of heat treatment are employed to ensure the high quality of the obtained indium antimonide film. The resultant indium antimonide film is then etched on with a circuit pattern. To improve the magnetoresistance value of the indium antimonide film element, short circuit electrodes are externally added or indium is devised to be precipitated within the indium antimonide film. The heat treatment for indium antimonide film commonly includes microzone melting or annealing. In the heat treatment of indium antimonide film, antimony is easily evaporated and as a result the composition and distribution of indium and antimony in the resultant indium antimonide film is frequently affected. To prevent the deterioration caused by the re-evaporation of antimony, an oxide layer is frequently covered on the indium antimonide film as a protective layer. In addition to the prevention of the re-evaporation of antimony, the protective layer is also considered effective for the prevention of the island-like indium aggregation caused by the surface tension of the melted surface in the microzone melting process. Due to poor adhesion caused by poor compatibility between the indium antimonide and the protective layer, the protective layer is easily damaged during the heat treatment, especially when the heat treatment temperature exceeds the melting point of indium antimonide. This further deteriorates the surface properties of indium antimonide and becomes an obstacle to the grain growth during re-crystallization. It is therefore unsatisfactory to prevent the re-evaporation of antimony by applying an oxide layer on the surface of indium antimonide film and a satisfactory process for producing indium antimonide film for magnetoresistance element is still lacking.
The sensitivity of indium antimonide film element can be improved by precipitating metallic short circuit electrode or short-circuiting the Hall voltage thereof to enhance the magnetoresistance resistance effect of the element in a magnetic field. However, as described above, the prior techniques employing stepwise film growth and microzone melting treatment fail to obtain satisfactory product. The precipitation of indium is usually uneven or emerges as large particulate aggregations. Even distribution of needle-like precipitate of indium cannot be controlled. Furthermore, the operation is quite complex. These and other factors render their large scale implementation impractical.